The present disclosure relates to a coordinate measuring machine, and more particularly to a portable articulated arm coordinate measuring machine having an adjustable counterbalance system.
Portable articulated arm coordinate measuring machines (AACMMs) have found widespread use in the manufacturing or production of parts where there is a need to rapidly and accurately verify the dimensions of the part during various stages of the manufacturing or production (e.g., machining) of the part. Portable AACMMs represent a vast improvement over known stationary or fixed, cost-intensive and relatively difficult to use measurement installations, particularly in the amount of time it takes to perform dimensional measurements of relatively complex parts. Typically, a user of a portable AACMM simply guides a probe along the surface of the part or object to be measured. The measurement data are then recorded and provided to the user. In some cases, the data are provided to the user in visual form, for example, three-dimensional (3-D) form on a computer screen. In other cases, the data are provided to the user in numeric form, for example when measuring the diameter of a hole, the text “Diameter=1.0034” is displayed on a computer screen.
An example of a prior art portable articulated arm CMM is disclosed in commonly assigned U.S. Pat. No. 5,402,582 ('582), which is incorporated herein by reference in its entirety. The '582 patent discloses a 3-D measuring system comprised of a manually-operated articulated arm CMM having a support base on one end and a measurement probe at the other end. Commonly assigned U.S. Pat. No. 5,611,147 ('147), which is incorporated herein by reference in its entirety, discloses a similar articulated arm CMM. In the '147 patent, the articulated arm CMM includes a number of features including an additional rotational axis at the probe end, thereby providing for an arm with either a two-two-two or a two-two-three axis configuration (the latter case being a seven axis arm).
The articulated arm may be of a variety of lengths, typically between two feet and four feet for example. To ease the use of the arm, a counter balance arrangement may be coupled to a fixed base to offset the torque applied by the weight of the articulated arm. The counter balance allows the articulated arm to be moved by the user with little effort and prevents the articulated arm from falling if released by the user. Unfortunately, in some circumstances the counter balance may apply too much, or too little torque due to differences in components, tolerances, configurations, and accessories of the articulated arm. As a result, rather than moving freely, the articulated arm may sag or resist movement depending on whether too little or too much counter balance is applied.
Accordingly, while existing articulated arms are suitable for their intended purposes what is needed is an AACMM having an improved adjustment and calibration of a counter balance for the articulated arm.